1. Technical Field
The present disclosure relates to a reflecting mask, an apparatus for fixing the reflecting mask and a method of fixing the reflecting mask. More particularly, the present disclosure relates to a reflecting mask used in a photolithography process using an extreme ultraviolet light beam, an apparatus for fixing the reflecting mask and a method of fixing the reflecting mask.
2. Discussion of Related Art
A size of a semiconductor device has been substantially reduced in order to achieve a high degree of integration. Thus, a photolithography process capable of achieving a high resolution has been required to manufacture a highly integrated semiconductor device. For example, an exposure process using deep ultraviolet employs a light having a wavelength of about 248 nm to expose a target having a size of about 250 nm to the light. The exposure process using the deep ultraviolet also employs a light having a wavelength of about 193 nm to expose a target having a size of about 100 to about 130 nm to the light. When an exposure process using an extreme ultraviolet light is employed, a target having a size of about 5 to about 70 nm is exposed to the light.
The exposure process using the extreme ultraviolet light is different from the exposure process using the deep ultraviolet light. Most material absorbs the extreme ultraviolet light, so that a reflecting mask is used instead of a transmitting mask to perform the exposure process using the extreme ultraviolet light. The reflecting mask generally includes a reflecting layer formed on a substrate and an absorbing layer pattern formed on the reflecting layer. The absorbing layer absorbs the extreme ultraviolet light. The reflecting layer has a multi-layered structure including other kinds of layers that are alternately formed. As one example, the reflecting layer includes a molybdenum (Mo) layer and a silicon (Si) layer. As another example, the reflecting layer includes a beryllium (Be) layer and a silicon layer.
The reflecting mask includes a conductive layer formed on a rear face of the substrate, and the conductive layer of the reflecting mask is fixed to an electrostatic chuck. The exposure process is performed in a state where the reflecting mask is fixed to the electrostatic chuck. In case that the fixed reflecting mask is not flat, a focus error and a pattern shift are generated on the substrate in the exposing process.